The present invention relates to a method for reducing a current break in a leg, not participating in the commutation, of a three-phase current block-fed synchronous machine while the leg currents of the two other legs are commutating. The present invention also relates to a circuit arrangement for carrying out the method.
A synchronous machine with trapezoidal electromotive force (EMF) generates a constant torque when fed with block or square wave shaped currents. For this reason, such a machine is employed in three phase feed drives. The block shaped currents are generated by means of a converter. A rotating field is generated in the machine by means of a control unit and a control voltage. In addition, the torque is proportional to the machine current. It has been found that breaks in the torque are caused by current breaks in a leg not participating in the commutation during the commutation of the other two leg currents of the three phase block current fed synchronous machine. These breaks are particularly noticeable at low speeds.